While prospecting in central Venezuela we chanced upon many artisanal miners in the bush.
You can see a family here working a shaft that was all of 50 ft straight down. Niches had been hand dug in the clay walls of the narrow shaft serving as the ladder going down. You would stretch out and basically walk straight down till you came to the adults they were working.
This I believe was one of the first photo's taken of Kimberlite found in this area in Venezuela. I was comfortable enough with going underground here, actually I could not stand it not to go check it out! They called the Kimberlite in this area Pintura. Which translates in spanish to colors. I actually held pieces with Diamonds in them.
~ Rob Towner
How Diamond-Bearing Kimberlites Reach the Surface of Earth: Acidification Provides the Thrust
Diamond-bearing kimberlites are volcanic rocks that originate deep in the Earth and are erupted onto the surface. LMU researchers have now shown that other rock types incorporated into the magma as it rises through overlying formations provide the necessary buoyancy for its long ascent.
Kimberlites are magmatic rocks that form deep in Earth's interior and are brought to the surface by volcanic eruptions. On their turbulent journey upwards magmas assimilate other types of minerals, collectively referred to as xenoliths (Greek for "foreign rocks"). The xenoliths found in kimberlite include diamonds, and the vast majority of the diamonds mined in the world today is found in kimberlite ores. Exactly how kimberlites acquire the necessary buoyancy for their long ascent through Earth's crust has, however, been something of a mystery.
(Science Daily - read entire article)